Ditetrazole substituted acridone compounds

ABSTRACT

Acridone and xanthone compounds substituted by at least one tetrazolyl group in one ring, and further substituted in the other ring, optionally for the acridones have antiallergic activity.

The invention relates to tricyclic compounds having medicinal properties, the synthesis of the compounds and their adaptation for medicinal use.

It has been found that tricyclic compounds of formula I defined hereinbelow are active in mammals and in in vitro mammalian preparations as inhibitors of allergic reactions associated with reaginic antibodies of the kind responsible for asthma in man, and that this effect is attributable to the suppression of the release of anaphylactic mediators.

In formula I ##STR1## at least one of Z¹ and Z² is a 5-(1-R)tetrazolyl or a 5-(2-R)tetrazolyl group wherein R is hydrogen or alkyl having 1 to 6 carbon atoms, and the other is selected from carboxy, 5-(1-R)tetrazolyl and 5-(2-R)tetrazolyl as defined;

Z³ is oxygen or a group NR¹ wherein R¹ is hydrogen or alkyl having 1 to 4 carbon atoms; and

WHEN Z³ is NR¹ as defined, Z² is also selected from hydrogen, nitro, cyano, halogen preferably chlorine or bromine, alkylsulphinyl, alkylsulphonyl, acyl, alkyl or alkoxy wherein the "alkyl" moiety of each of the acyl, alkyl, alkoxy, alkylsulphinyl, and alkylsulphonyl groups has 1 to 6 carbon atoms;

TOGETHER WITH SALTS, AND WHERE ONE OF Z¹ or Z₂ is carboxyl, amides and esters of said compounds.

Compounds of formula I include 2-Z¹,6-Z² -xanthones, 2-Z¹,6-Z² -acridones and 2-Z¹,7-Z² -N-alkylacridones in which compounds at least one of Z¹ and Z² is 5-tetrazolyl and the other is selected from 5-tetrazolyl and carboxy, together with salts of said compounds.

Esters of compounds of formula I include alkyl esters having 1 to 6 carbon atoms, and amides include N-alkyl- and N,N-dialkylamides wherein the alkyl groups have 1 to 6 carbon atoms.

The inhibition activity of the compounds of formula I has been demonstrated (a) in tests using the response of passive cutaneous anaphylaxis (PCA test) in which is measured the skin reaction produced as the result of interaction between specific antigen injected intravenously and cell-fixed reaginic antibody previously injected into the skin of a mammal (see for example Z. Ovary: Fedn. Proc. Am. Soc. exp. Biol. 24, 94 (1965)), (b) by measurement of the amount of histamine released after antigen challenge of peritoneal mast cells from actively sensitised rats (see for example, 1. Acta Pharmacol. et Toxicol. 30, supp. 1 (1971), 2. Thorax, 27/1, 38 (1972), and (c), by measurement of the histamine released from human chopped lung tissue passively sensitised in vitro with reaginic antibody when challenged with the homologous antigen (Br. Med. J. 3,272 (1968)). The activity of acids of formula I has been demonstrated as described hereinabove using solutions of the carboxylate anion.

For the sake of convenience, compounds of formula I wherein either of Z¹ and Z² is an alkyl carboxylate group, shall hereinafter be referred to as `esters` of formula I. Similarly references to `amides` of formula I shall be construed as references to compounds of formula I wherein one of Z¹ and Z² is an optionally substituted carboxamide, and references to `salts` of formula I shall mean compounds of formula I wherein one or both of Z¹ and Z² is a carboxylate or tetrazolyl salt group.

Pharmaceutically acceptable salts of formula I include ammonium salts, alkali metal salts such as sodium and potassium salts, alkaline earth salts such as magnesium and calcium salts, and salts of organic bases, for example, amine salts such as triethanolamine and diethylaminoethylamine salts, and piperazine and morpholine salts. Especially valuable are water soluble salts of formula I most preferably those having a solubility in water of at lest 1 mg/ml.

The anti-allergic activity of the salts of formula I lies in the anion and the nature of the cation does not contribute to the activity, but for medicinal purposes the cation must of course be pharmaceutically acceptable.

Pharmaceutically acceptable cations in compounds of formula I include hydrogen, ammonium, alkali metal cations such as sodium and potassium, alkaline earth metal cations such as calcium and magnesium and organic base cations, for example, alkylammonium cations of such alkylamines as triethanolamine and diethylaminoethylamine, piperazinium and morpholinium cations.

Suitable substituted carboxamide groups include N-alkyl and N,N-dialkyl substituted carboxamide groups wherein the alkyl moiety is an alkyl group having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms.

Preparation of compounds of formula I may be effected by any method known in the art of preparing them and compounds of analogous chemical structure. In general the compounds of formula I wherein one of Z¹ and Z² is a carboxylate derivative (for example an amide, ester or salt), are prepared by suitable treatment of the corresponding acid. However, in certain circumstances it is possible to prepare such derivatives without prior isolation of the carboxylic acid, either by the choice of suitable reactants or by forming the desired derivative in a reaction mixture of the acid, without first isolating the acid.

Methods for the preparation of compounds and salts of formula I are described hereinbelow, but it will be understood that in some instances the methods may be adopted to yield the corresponding esters or amides of formula I

1. hydrolysis of a compound of formula II ##STR2## wherein one of Y¹ and Y² is a carboxyl group precursor, such as a nitrile group, trichloromethyl group or a group COL¹ wherein L¹ is a leaving group, such as a nucleophilic atom or group, for example, a trichloromethyl group, an optionally substituted amino group, a halogen atom or an alkoxy group; and the other of Y¹ and Y² is the group Z¹ or Z², as appropriate, as defined in formula I; and Z³ has the meaning defined in formula I. Hydrolysis is conveniently effected by heating a compound of formula II with a dilute aqueous alkali, or with a dilute aqueous mineral acid optionally with an organic acid. For example, one may use dilute sulphuric acid, dilute hydrochloric acid with acetic acid, or dilute aqueous sodium hydroxide solution. Hydrolysis with aqueous alkali will yield inter alia an aqueous solution of a dicarboxylate salt but if it is desired to collect the maximum amount of carboxylic acid, then the reaction mixture should be acidified when hydrolysis is completed to precipitate the acid. On the other hand if the desired end-product is the carboxylate salt, then following hydrolysis, the cation of the desired salt may be added to precipitate the desired salt by the common ion effect without prior isolation of the corresponding acid.

By means of nucleophilic substitution reactions analogous to hydrolysis, for example, alcoholysis and ammonolysis, compounds of formula I other than the carboxylic acid may be prepared directly from compounds of formula II. Thus reaction of a compound of formula II with an appropriate alcohol yields an ester of formula I, and reaction with ammonia or an appropriate primary or secondary amine yields an amide of formula I.

2. cyclisation of a compound of formula III ##STR3## wherein Z¹, Z² and Z³ have the meaning defined in formula I and Q is a hydroxyl, alkoxy or an optionally substituted amino group, a halogen atom, or a RCO₂ group, a ROCO₂ group or a RSO₃ group wherein R is alkyl or aryl. Cyclisation may be effected by heating a compound of formula III at an elevated temperature, for example up to about 300° C. Preferably heating is carried out in the presence of a Lewis acid under anhydrous conditions or a protonic acid, optionally in the presence of a non-polar solvent. Preferred Lewis acids include boron trifluoride and aluminium trichloride and preferred protonic acids include sulphuric, hydrochloric and polyphosphoric acids.

If, however, Z² is a carboxylate substituent in the 5-position of the nascent compound of formula I, reaction conditions and/or the group Q must be chosen so as to avoid reaction of the group Z².

3. oxidation of a compound of formula VIII ##STR4## wherein one of W¹ and W² is a lower alkyl group or a group C(:O)R wherein R is an optionally substituted lower alkyl group having 1 to 4 carbon atoms, or is OH, and the other of W¹ and W² is Z¹ or Z², as appropriate, as defined in formula I; and Z³ is as defined in formula I. Oxidation of compounds wherein W¹ and/or W² are lower alkyl groups may be effected with such conventional oxidising agents as acid or alkaline aqueous potassium permanganate solution; chromium trioxide, for example, with acetic acid or sulphuric acid; oxygen in the presence of a conventional catalyst such as lead, cobalt and manganese salts, for example, lead acetate; or aqueous solutions of sodium dichromate.

Oxidation of compounds wherein W¹ or W² are the groups C(:O)R may be effected with such conventional oxidising agents as chromium trioxide, for example, with acetic acid or sulphuric acid; aqueous solutions of salts of hypochlorous and hypobromous acids in the presence of a base; sodium or potassium dichromate with acetic acid; or nitric acid. These oxidation procedures are advantageously effected with heating in the liquid phase.

4. Oxidation of a compound of formula IX ##STR5## wherein Z¹ and Z² have the meaning defined hereinbefore in formula I, Y³ is a group Z³ as defined hereinbefore in formula I and Y⁴ is a methylene group; or Y⁴ is selected from CH and CR wherein R is lower alkyl and Y³ is N. Oxidation of compounds of formula IX may be effected with such conventional oxidising agents as nitric acid; aqueous solutions of hypochlorous and hypobromous acids in the presence of base; chromium trioxide, for example with acetic acid or with sulphuric acid; or aqueous solutions of sodium dichromate.

Oxidation of compounds of formula IX wherein Y⁴ is a methylene group and Y³ is oxygen or NR wherein R is alkyl having 1 to 4 carbon atoms, or Y⁴ and Y³ are each CH, may also be effected with such conventional oxidising agents as oxygen in the presence of triton B in pyridine solution; or oxygen in the presence of potassium t-butoxide in the presence of t-butanol and dimethylsulphoxide.

Compounds analogous to the compounds of formula IX wherein either of Z¹ and Z² is replaced by a group W¹ or W², as appropriate, as defined in formula VIII, may also be oxidised so as to produce carboxylic acids or salts of formula I. Oxidation in the case of such compounds may be effected with such conventional oxidising agents as chromium trioxide, for example, with acetic acid or with sulphuric acid; or aqueous solutions of sodium dichromate. In the case of such compounds wherein either of W¹ and W.sup. is alkyl, oxidation may also be effected with such conventional oxidising agents as aqueous solutions of salts of hypobromous or hypochlorous acids in the presence of a base; or nitric acid. Advantageously any of the hereinbefore described oxidation procedures wherein aqueous solutions of sodium dichromate are employed, are carried out at an elevated temperature in a sealed container. Oxidation of the groups W¹ and W² in such a case is preferably effected at a temperature of from 200° to 210° C. Oxidation of the xanthone nucleus in such a case is preferably effected at a temperature of from 240° to 260° C.

5. Cyclisation of a compound of formula (X) ##STR6## wherein Z¹ and Z² have the meaning defined hereinbefore in formula I and Z⁴ is a hydroxyl group or a group NHR¹ wherein R¹ is hydrogen or alkyl having 1 to 4 carbon atoms and X is a leaving group, for example, a halogen for example chlorine; hydroxyl; p-toluenesulphonyloxy; nitro; or sulphinate. Cyclisation may be effected by heating a compound of formula (X) wherein X is other than nitro at an elevated temperature up to about 120° C., in the presence of an alkaline hydroxide such as sodium hydroxide and optionally in the presence of a polar solvent such as water or aqueous ethanol. Where X is a nitro group cyclisation may be advantageously effected in a dipolar aprotic solvent such as dimethyl sulfoxide, dimethyl acetamide, N-methyl-2-pyrrolidone sulfolane, hexamethylphosphoramide, dimethyl formamide and acetonitrile, at an elevated temperature of from 50° to 150° C. preferably from 100° to 120° C.

Alternatively a compound of formula(X) wherein one of Z¹ and Z² is replaced by a carboxyl group precursor Y¹ as defined hereinbefore, and X is other than nitro, may be simultaneously cyclised and hydrolysed. Such a reaction may be effected by heating such a compound of formula(X) at an elevated temperature, up to about 120° C., in the presence of an alkaline hydroxide such as sodium hydroxide and optionally in the presence of a polar solvent such as water or aqueous ethanol. N-alkyl acridone esters of formula I may also be prepared by alkylation of corresponding acridone compounds of formula I. Alkylation may be effected by any conventional process for alkylation of secondary amino groups, for example, by reaction with a group RX⁵ wherein R is alkyl having 1 to 6 carbon atoms and X⁵ is a leaving group such as a halogen atom, in the presence of a strong base. Suitable bases are sodamide and sodium hydride. Desirably alkylation is effected in the presence of a solvent which includes dimethyl sulphoxide xylene, or liquid ammonia.

The compounds of formula I may also be prepared by formation of a 5-tetrazolyl group as the final step. Thus in formula I wherein one or both of Z¹ and Z² are tetrazolyl or (1-alkyl)tetrazolyl groups, these compounds may be prepared by reaction of hydrazoic acid or a salt thereof or nitrous acid with an appropriate compound of formula XIV wherein ##STR7## Y⁷ is a group Z¹ as defined in formula I or a tetrazolyl group precursor and Y⁸ is a group Z² as defined in formula (I) or a tetrazolyl group precursor, provided that at least one of Y⁷ and Y⁸ is a tetrazolyl group precursor.

When hydrazoic acid or a salt thereof is used, a suitable tetrazolyl group precursor is a group ##STR8## wherein R³ and R⁴ together form a bond (nitrile), R³ is hydrogen or alkyl and R⁴ is alkoxy having 1 to 6 carbon atoms (imidoester), thioalkyl having 1 to 6 carbon atoms (imidothioester), --NH--NH₂ (amidrazone), or amino (amidine) or R³ is hydroxy and R⁴ is amino (amidoxime), or R³ is alkyl and R⁴ is halogen (imidohalide). In the case of amidoximes and nitriles, only tetrazolyl compounds may be produced and in the case of imidohalides only alkyltetrazolyl compounds may be produced. The reaction is preferably carried out in a polar aprotic liquid medium using a salt of hydrazoic acid.

When nitrous acid is used, a suitable tetrazolyl precursor group is a group ##STR9## wherein R³ is hydrogen or alkyl and R⁴ is --NH--NH (amidrazone) or R³ is hydrogen and R⁴ is amino (amidine). In the latter case, reduction of the intermediate nitrosation product, with or without prior isolation, using for example sodium amalgam, is required to give the corresponding tetrazolyl compound.

The tetrazolyl compounds of formula I thus prepared may be isolated as the free acid or as a tetrazolyl salt, and the one converted to the other in known manner and as specifically described below in relation to the carboxylic acids of formula I and their salts.

The 5-(1- and 2- alkyl)tetrazolyl compounds of formula I may be made from the corresponding tetrazolyl compounds of formula I or their salts by alkylation.

Salts of formula I may be isolated from a reaction medium by any conventional process for the isolation of salts from a solution thereof in a polar medium.

Desirably the salts of formula I are purified prior to incorporation in a pharmaceutical composition by any conventional method.

Esters and amides of acids of formula I may be prepared by any conventional method including esterification of the acid or acid chloride with an alkyl or aryl alcohol to yield the corresponding alkyl or aryl ester respectively and reaction of the acid or acid chloride with ammonia or an amine to yield the corresponding amide or substituted amide respectively. Compounds of formula I where Z¹ and Z² are different and are chosen from acid, ester, amide and salt functions, may be prepared by the above methods, and by partial hydrolysis, where appropriate.

The compounds of formula I are useful in the treatment or prophylaxis of mammalian allergic conditions such as asthma and other allergic chest conditions, hay fever (allergic rhinitis), conjunctivitis, urticaria and eczema. In particular they are of value in reaginic mediated Type I hypersensitivity asthma (`extrinsic asthma`) and the so-called `intrinsic asthma` in which no sensitivity to extrinsic antigen can be shown.

The magnitude of a prophylactic or therapeutic dose of compound of formula I will of course vary with the nature of the severity of the allergic condition to be treated and with the particular compound of formula I and its route of administration. In general the dose range lies within the range of 2 μg. to 100 mg. per Kg. body weight of a mammal.

In the case of an allergic condition as defined hereinbefore, for example, allergic asthma, a suitable dosage is from 20 μg. to 0.5 mg., for example about 0.1 to 0.5 mg., of a compound of formula I, per Kg. of bodyweight of the patient undergoing treatment, when pulmonary administration as described hereinafter is employed. In the case where a composition for intravenous administration is employed a suitable dosage range is from 0.2 to 10 mg. (preferably 1 to 5 mg.) of a compound of formula I per Kg. of bodyweight of patient, and in the case where an oral composition is employed a suitable dosage range is from 1 to 50 mg. of a compound of formula I per Kg. of bodyweight of a patient, preferably from 10 to 40 mg/Kg.

In the case where a composition for nasal and ocular administration is employed, for example, in the treatment of allergic rhinitis, a suitable dose is from 0.5 to 25 mg. of a compound of formula I per patient.

The pharmaceutical compositions of the present invention comprise a compound of formula I as an active ingredient, and may also contain pharmaceutically acceptable carrier and optionally other therapeutic ingredients. The compositions include compositions suitable for oral, rectal, opthalmic, pulmonary, nasal, dermal, topical, or parenteral (including subcutaneous, intramuscular and intravenous) administration, although the most suitable route in any given case will depend on the nature and severity of the condition being treated, and on the nature of the active ingredient. They may be conveniently presented in unit dosage form and prepared by any of the methods well known in the art of pharmacy.

Pharmaceutical compositions of the present invention suitable for oral administration may be presented as discrete units such as capsules, cachets or tablets each containing a predetermined amount of the active ingredient; as a solution or a suspension in an aqueous liquid, a non-aqueous liquid, an oil-in-water emulsion or a water-in-oil liquid emulsion. Such compositions may be prepared by any of the methods of pharmacy but all methods include the step of bringing into association the active ingredient with the carrier which constitutes one or more accessory ingredients. Desirably, each discrete unit contains from 50 mg. to 500 mg. of the active ingredient.

A valuable form of a pharmaceutical composition of the present invention, for use in the treatment of allergic asthma, is one suitable for pulmonary administration via the buccal cavity. Preferably the composition is such that particles having a diameter of 0.5 to 7μ, most preferably 1 to 6μ, containing active ingredient, are delivered into lungs of a patient. Such compositions are conveniently in the form of dry powders for administration from a powder inhalation device or self-propelling powder-dispensing containers; preferably the powders comprise particles containing active ingredient of which particles at least 98% by weight have a diameter greater than 0.5μ and at least 95% by number have a diameter less than 7μ. Most desirably at least 95% by weight of the particles have a diameter greater than 1μ and at least 90% by number of the particles have a diameter less than 6μ.

The compositions in the form of dry powders preferably include a solid fine powder diluent and are conveniently presented in a pierceable capsule, for example of gelatin.

Self-propelling compositions of the invention may be either powder-dispensing compositions or compositions dispensing the active ingredient in the form of droplets of a solution or suspension. Self-propelling powder-dispensing compositions include a liquid propellant having a boiling point of below 65° F. at atmospheric pressure. Generally the propellant may constitute 50 to 99.9% w/w of the composition whilst the active ingredient may constitute 0.1 to 20% w/w, for example, about 2% w/w, of the composition. The carrier in such compositions may include other constituents, in particular a liquid non-ionic or solid anionic surfactant, or a solid diluent (preferably having a particle size of the same order as of the particles of active ingredient) or both. The surfactant may constitute up to 20% w/w, though preferably it constitutes below 1% w/w of the composition.

Self-propelling composition wherein the active ingredient is present in solution comprise an active ingredient, propellant and co-solvent, and advantageously an antioxidant stabiliser. The co-solvents may constitute 5 to 40% w/w of the composition, though preferably less than 20% w/w of the composition.

Compositions of the present invention may also be in the form of aqueous or dilute alcoholic solution, optionally a sterile solution, of the active ingredient for use in a nebuliser or atomiser.

Compositions of the present invention suitable for parenteral administration conveniently comprise sterile aqueous solutions of the active ingredient, which solutions are preferably isotonic with blood of a patient under treatment.

Pharmaceutical composition of the present invention suitable for topical use include compositions suitable for administration to the skin, eyes, nose and mouth. Compositions for use on the skin include lotions and creams comprising liquid or semi-solid emulsions, either oil-in-water or water-in-oil, and ointment, preferably containing from 0.2 to 5% w/v of the active ingredient. Desirably the creams and ointments should contain a preservative such as methyl hydroxybenzoate.

Compositions for administration to the eye include eye drops comprising the active ingredient in aqueous or oily solution and ointments, preferably containing 0.2 to 5% w/v of the active ingredient. The eye drops are desirably fungistatic and bacteriostatic and are preferably prepared sterile.

Compositions suitable for administration to the nose include powder, self-propelling and spray compositions similar to those already described under compositions suitable for pulmonary administration but having when dispersed, a somewhat larger particle size of the order of 10 to 200 microns. Other compositions suitable for nasal administration include a coarse powder having a particle size of 20 to 500 microns which is administered in the manner in which snuff is taken i.e. by rapid inhalation through the nasal passage from a container of the powder held close up to the nose. Another composition suitable for nasal administration is nasal drops comprising 0.2 to 5% w/v of the active ingredient in aqueous or oily solution.

Compositions suitable for topical administration in the mouth include lozenges comprising 10 to 100 mg. of the active ingredient in a flavoured base, usually sucrose and acacia or tragacanth; and pastilles comprising 10 to 100 mg. of the active ingredient in an inert base such as gelatin and glycerin; or sucrose and acacia.

Other therapeutic ingredients suitable for inclusion in the hereinbefore described compositions, especially in the case of those compositions intended for use in the treatment of allergic asthma, include bronchodilators such as isoprenaline, adrenaline, orciprenaline, isoethanine and physiologically acceptable acid addition salts thereof, especially isoprenaline sulphate. Conveniently the bronchodilator is present in an amount of 0.1 to 50% w/w of the weight of active ingredient present.

Included within the scope of the present invention, but in no way limited thereto, are the following specific features:

1. A compound of formula I as defined hereinabove, where novel.

2. The synthesis of compounds of formula I as defined hereinabove, by any method known in the art for preparing them and compounds of analogous chemical structure.

3. Pharmaceutical compositions comprising a compound of formula I as defined hereinabove in association with a pharmaceutically acceptable carrier therefor.

4. The preparation of pharmaceutical compositions comprising a compound of formula I as defined hereinabove as an active ingredient, by any conventional method, including admixture of the ingredients.

5. A method of treatment or prophylaxis of mammalian allergic conditions comprising administration of a therapeutic or prophylactic dose respectively, of a compound of formula I as defined hereinabove.

Set forth below are examples of this invention.

EXAMPLE 1 Preparation of 2,6-Di-(5-tetrazolyl)xanthone

2,6-Dicyanoxanthone (alternative Nomenclature 9-oxaxanthene-2,6-dicarbonitrile), prepared (a) by application of the Sandmeyer process to 2,6-diaminoxanthone, or (b) by dehydration of xanthone-2,6-dicarboxamide with thionyl chloride in dimethyl formamide at -65° C., was heated in dimethyl formamide with sodium azide (1 part) and ammonium chloride (1 part) at 115° C. for 24 hours. On addition of water and dilute by hydrochloric acid there was obtained 2,6-di-(5-tetrazolyl)xanthone, m.p. >400°, which was insoluble in most organic solvents but which dissolved readily in dilute sodium bicarbonate solution.

EXAMPLE 2 Preparation of 2,6-Di-(5-tetrazolyl)acridone

2,6-Diamino acridone was converted by the Sandmeyer diazotisation process into acridone-2,6-dicarbonitrile, m.p. >350° C. To a suspension of sodium azide (0.52g.) and ammonium chloride (0.43g.) in dry dimethyl formamide (10 ml.) was added 0.98g. of the dicarbonitrile after 8 hours heating at 100° C. The reaction mixture was poured into dilute hydrochloric acid containing ice and the precipitate recovered. Crystallisation from dimethyl formamide gave 2,6-di-(5-tetrazolyl)acridone, m.p. >400° C.

EXAMPLE 3 10-Methyl-2,7-di-(5-tetrazolyl)acridone

By a similar process to Example 2, 10-methyl acridone-2,7-dicarbonitrile gave 10-methyl-2,7-di-(5-tetrazolyl)acridone, m.p. >400° C.

The dicarbonitrile intermediate was prepared from 2,7-diamino-N-methyl acridone by the Sandmeyer reaction.

EXAMPLE 4 Preparation of 2,6-di-(5-tetrazolyl)acridone disodium salt

2,6-Di-(5-tetrazolyl)acridone (0.2 g) was suspended in water (10 ml) and treated with N aqueous sodium hydroxide solution (1.2 ml). The mixture was evaporated to 5 ml and ethanol added to crystallise out the disodium salt which was dried under phosphorus pentoxide. The salt did not melt at 470° C. and was hygroscopic.

EXAMPLE A -- Powder Capsules for Inhalation

    ______________________________________                                         2,6-Di-(5-tetrazolyl)acridone                                                  disodium salt (0.5-7.0 μm powder)                                                                    4      mg                                             Lactose (30-90 μm powder)                                                                            46.0   mg                                             ______________________________________                                    

The powders were mixed until homogeneous and filled into suitably sized hard gelatin capsules, 50 mg of mixture per capsule.

EXAMPLE B -- Injection Solution

    ______________________________________                                         2,6-Di-(5-tetrazolyl)acridone                                                  disodium salt            50     mg                                             Water for Injections B.P.   to                                                                          1.0    ml                                             ______________________________________                                    

The disodium salt was dissolved in half of the Water and then made up to volume and sterilised by filtration. The resulting solution was distributed into ampoules under aseptic conditions.

EXAMPLE C -- Inhalation Aerosol

    ______________________________________                                         2,6-Di-(5-tetrazolyl)acridone                                                  (0.5 - 7.0 μm powder)                                                                               200     mg                                             Sorbitan Trioleate      100     mg                                             Saccharin Sodium                                                               (0.5 - 7.0 μm powder)                                                                               5       mg                                             Menthol                 2       mg                                             Trichlorofluoromethane  4.5     g                                              Dichlorodifluoromethane 10.0    ml                                             ______________________________________                                    

The Sorbitan Trioleate and Menthol were dissolved in the Trichlorofluoromethane. The Saccharin Sodium and the diacid

were dispersed in the mixture which was then transferred to a suitable aerosol canister and the Dichlorofluoromethane injected through the valve system. This composition provides 2 mg. of Acid in each 100 μl. dose. 

What I claim is:
 1. 2,6-Di-(5-tetrazolyl)acridone and pharmaceutically acceptable salts thereof.
 2. 10-Methyl-2,7-di-(5-tetrazolyl)acridone and pharmaceutically acceptable salts thereof.
 3. An alkali metal salt of 2,6-di-(5-tetrazolyl)acridone.
 4. 2,6-Di-(5-tetrazolyl)acridone disodium salt.
 5. A tricyclic compound of formula ##STR10## wherein Z³ is a group NR¹ in which R¹ is hydrogen or alkyl having 1 to 4 carbon atoms, and wherein Z¹ and Z² are 5 - tetrazolyl groups together with pharmaceutically acceptable salts of said compound.
 6. A tricyclic compound of the formula (I) ##STR11## in which both Z¹ and Z² is a 5-(1-R)tetrazolyl or a 5-(2-R)tetrazolyl group in which R is hydrogen or alkyl having 1 to 6 carbon atoms; Z³ is a group NR¹ in which R¹ is hydrogen or alkyl having 1 to 4 carbon atoms; and pharmaceutically acceptable salts thereof.
 7. A tricyclic compound of the formula (I) ##STR12## wherein one of Z¹ and Z² is a 5-(1-R) tetrazolyl or a 5-(2-R) tetrazolyl group in which R is hydrogen or alkyl having 1 to 6 carbon atoms, and the other is selected from 5-(1-R) tetrazolyl and 5-(2-R) tetrazolyl as defined; together with pharmaceutically acceptable salts, and where in Z³ is NH and Z² is a substituent as defined in the 6-position. 